1) Field of the Invention
The present invention relates to a data-duplication control apparatus that performs a control for a duplication process of duplicating data stored in a storage device constituting a redundant-array-of-independent-disks (RAID), and more particularly, to a data-duplication control apparatus that can execute a redundant copy of data when hard disk devices of different RAID types are used in a combined manner.
2) Description of the Related Art
Conventionally, a RAID system realizes an improvement of performance, such as a speed of reading and writing data, an increase of storage capacity, and an improvement of reliability by combining a plurality of hard disk devices.
The RAID system is designed in such a manner that data is saved even if there is a failure in one of the hard disk devices constituting the RAID system. For example, in RAID1 and RAID0+1, the same data is redundantly stored in two hard disk devices.
Furthermore, in RAID2, RAID3, RAID4, and RAID5, error check and correction (ECC) information and parity information are written in other hard disk device to recover data of a hard disk device having a failure, even when a failure has occurred in one hard disk device.
However, in the RAID 1 and the RAID0+1, the redundancy of data is lost if a failure has occurred in one of the hard disk devices in which the same data is stored.
To prevent such problems, a method called redundant copy has been developed. In the redundant copy, a copy of data stored in a hard disk device is created in a backup hard disk device in preparation for an occurrence of a failure in the hard disk device (see, for example, Japanese Patent Application Laid-Open Publication No. Hei8-249133).
However, because the conventional technology described above sets a copy-source hard disk device for the redundant copy in a fixed manner, it is not possible to perform the redundant copy effectively.
In other words, because the copy-source hard disk device is determined regardless of the RAID type such as RAID1, RAID0+1, and RAID5 when hard disk devices of different RAID types are used in a combined manner, the redundant copy may have failed or a load on a RAID device may have increased when performing the redundant copy.
For example, the same data is stored in two hard disk devices in the RAID1 or the RAID0+1, however, if a hard disk device that is anticipated to have a failure is set to a copy source in a fixed manner, a risk of having a failure in the hard disk device at a time of performing the redundant copy becomes high.
In the RAID5, the parity information that is used to recover data stored in a hard disk device having a failure is stored in a plurality of hard disk devices in a distributed manner, and when a failure has occurred in one hard disk device, data is recovered from the parity information stored in other hard disk device.
Although it is possible to perform a redundant copy to create a copy of data stored in a hard disk device in other hard disk device using the parity information, the recovery of data using the parity information is not desirable because it causes a considerable load to the RAID device.
For this reason, it is extremely important how to perform a redundant copy of data effectively when hard disk devices of different RAID types are used in a combined manner.